1. Field of the Invention
This invention relates to a method of electroslag welding.
2. Description of the Prior Art
Difficulties have been encountered in the prior art when attempting to join by welding members formed of low alloy, high tensile strength steels of the family of steels which includes American Society of Testing Materials designations ASTM A516-76 (boiler or pressure vessel type steel), ASTM A572-76 (structural plate steel) and ASTM A216-75 (cast steel). In the prior art, when it has been attempted to provide an electroslag weld between steel members of the family of low alloy, high tensile strength steels such as those described, the resulting electroslag weld between the high tensile strength members has resulted in two basic problems, as follows:
(1) loss of impact strength in the weld deposit, i.e., poor resistance of the weld to low stress brittle fracture; and
(2) low ductility of the weld.
The foregoing described undesirable characteristics of electroslag welds between members of low alloy, high tensile strength materials such as those enumerated could be overcome in the prior art only by the use of a prolonged post-weld "normalizing" high temperature heat treatment of the total welded part with subsequent cooling of the welded member in air or liquid. The purpose of this prior art post-weld normalizing heat treatment of the total welded part subsequent to the completion of the weld is to improve to acceptable values the mechanical properties of the weld deposit, including the tensile strength, impact strength, and ductility of the weld deposit. Typically, the prior art normalizing heat treatment just mentioned is conducted at a temperature such as 1600 degrees F. for a time period such as for four hours, after which the welded member is cooled by liquid or air to a temperature such as 400 degrees F.
It is obvious that the post-weld "normalizing" heat treatment required in the prior art in connection with welds in the ASTM A516-76 family of steels as just described is extremely expensive due both to furnace cost and to fuel cost, and to such an extent that such cost is prohibitive.
To the best of my knowledge, prior to my invention there was no welding electrode known or available which could be used for the electroslag welding of steels of the ASTM A516-76 family in which the resulting electroslag weld deposit did not require the post-weld high temperature normalizing heat treatment hereinbefore described in order to obtain acceptable mechanical properties in the weld deposit.
In addition to the "normalizing" post-weld heat treatment just described which was necessary in the prior art to obtain acceptable mechanical properties when welding low alloy, high tensile strength steel members of the type hereinbefore described, it is also the general practice to provide a stress relief heat treatment at a temperature such as 1150 degrees F. The purpose of the stress relief treatment is to equalize the tensile and compressive stresses set up during the welding operation. This stress relief treatment just described is standard practice subsequent to the completion of a weld and is utilized in welded members produced by use of the electrode and welding method of the present invention. However, as will be pointed out in more detail hereinafter, use of the welding electrode and welding method of the present invention eliminates the need for the extremely expensive and energy consuming high temperature (such as 1600 degrees F.) post-weld "normalizing" heat treatment of welded parts which has been required in the prior art for electroslag welds between low alloy, high tensile strength steels of the type hereinbefore described.
A problem which has presented itself in the prior art in connection with the formulation of welding electrode chemistry is the fact that a change in the electrode chemistry which tended to increase the impact strength of the resulting electroslag weld, such as a decrease in the carbon content of the welding electrode, at the same time tended to decrease the tensile strength of the resulting electroslag weld to an unacceptable value; and conversely, a change in the electrode chemistry, such as an increase in the carbon content of the electrode, which tends to increase the tensile strength of the resulting electroslag weld at the same time tends to decrease the impact strength of the resulting electroslag weld.
In this specification, in order to achieve brevity of expression, the abbreviation ASTM will be used to designate "American Society of Testing Materials." Also, the expression "A516-76 family" will be used to designate low alloy, high tensile strength steels of any of the types and ASTM designations just enumerated (i.e., ASTM A516-76, ASTM A572-76 and ASTM A216-75). Also, the abbreviation "PSI" will be used to designate "pounds per square inch."